or does it also depend on other stuff (like peeks in color spectrum, etc.)?

Color temp. is not an accurate way to select bulbs for a planted tank. You want bulbs with peaks in the blue and red spectrum. Check out the post at the top of the lighting section titled "Lumens and PAR" for more specific info.

Thanks Marcel. I appreciate that plants need light that peeks in red and blue regions. But I wanted to know how we can determine the color of a bulb (regardless of the intensity or appropriateness).

Tell you why I'm asking. I needed to replace my florescent bulb, and was deciding between a 6500K and a 5300K. The spectra distribution of both lamps seemed pretty close. I went with the 6500K because I thought it'd be bluer, I like a little hint of blue. But it's actually pretty yellow...

The guy at LFS tells me the 5300K is bluer than the 6500K. But that doesn't make sense to me.
Thanks

The Kelvin rating is merely an indicator of the color that the bulb will appear to our eyes. The popular Perfecto strip with 9325K Power Compact bulbs is more red/violet to the eye than most 6500K Power Compact bulbs.

As a rule of thumb, higher Kelvin bulbs tend to be more blue in appearance but each bulb is different. It's best to find an example and see for yourself.

The guy at your LFS is mistaken. I like the bluer bulbs, particularly 6500Ks and up. 5300K looked WAY too yellow for me. Now I'm running one of both but will go with two 6500Ks when it's time to replace. I'm also thinking about adding a third 55 Watt strip when I get some extra money (yeah, right...hahaha), but that's another story...

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